Heat can cause solid propellant to autoignite, causing the motor to explode, burst or move. In order to improve safety of solid propellant motors a relatively new requirement, referred to as "insensitive munitions cook-off test" (hereinafter "I.M. testing"), will soon be standard for all rocket motors. The test consists of heating the motor until autoignition occurs. To pass the test the ignited motor must remain passive while the propellant burns off, with no explosion, shrapnel or propulsion. This test ensures the safety of motors in case of fire or heat.
Current solid propellant rocket motors are not designed to withstand I.M. testing. Consequently, if a motor is subjected to cook-off temperatures, autoignition occurs, and the motor either explodes, bursts or becomes propulsive. This results because the motor is unable to relieve pressure build-up from the ignited propellant.